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1.
The salient features of the total low energy inelastic electron scattering cross section in transition metals are described by a constant term σ0 plus a term σd that is proportional to the number of unoccupied d-orbitals. This simple model predicts that low energy electrons transmitted through a ferromagnetic ultrathin film acquire a transport spin polarization a(χ). Using the ratio σ0/σd as the only adjustable parameter, the model predicts the enhancement of the spin polarization of the low energy cascade electrons as well as a(χ) in reasonable agreement with the existing observations on Fe, Co and Ni. A detector for electron spin polarization P based on the spin dependent transmission of electrons through ferromagnetic material is proposed which should be superior to existing P-detectors by 1–2 orders of magnitude. 相似文献
2.
The spin polarization of secondary electrons with nearly zero kinetic energy from Fe (100) and Co (100), excited with photons of energy between 20 and 60 eV, was found to be 45%±5% for Fe and 35%±5% for Co. This value is higher than the average valence band spin polarization Pb=nb/n=2.2/8=27% and 1.7/9=19% for Fe and Co, respectively. With increasing kinetic energy, the spin polarization of the secondaries decreases to the value of Pb within the first 5 eV, remaining constant (within statistical error) at higher kinetic energies. As a spin dependent scattering process we propose excitations within the d-bands, which can be shown to be asymmetric with respect to the electron spin. The high net spin polarization of the slowest emitted electrons is obtained by filtering out monitory-spin electrons at the vacuum barrier. 相似文献
3.
Two polarization phenomena in Compton scattering by polarized electrons were investigated. In the first experiment, the rotation of the polarization plane of photons passing through magnetized iron and gadolinium was measured. This effect arises from a spin dependence of the Compton forward scattering amplitude. For 228 and 333 keV photons and iron absorbers, the observed rotation angles areφ 0=(3.90±0.57) ×10?3 rad · cm?2 and (4.75±0.58)×10?3 rad · cm?2, respectively. Secondly, the orientation of the photon polarization plane after scattering of unpolarized photons by polarized electrons was measured. This experiment tests time reversal invariance in quantum electrodynamics. No dependence of the polarization plane on the direction of the electron spin was found within 2×10?3. 相似文献
4.
Wilfried Hilgner Joachim Kessler Ernst Steeb 《Zeitschrift für Physik A Hadrons and Nuclei》1969,221(4):305-323
Cross sections and spin polarization of low-energy electrons scattered by I2 and C2H5I molecules were measured in the energy range from 200 to 600 eV and angular range from 30 to 150°. At the same time, several authors made calculations of cross sections and polarizations based on the following assumptions: The molecule consists of free atoms which are independent of each other (the influence of binding is negligible) and scattering of an electron does not occur more than once within the molecule. The agreement between theory and experiment in a wide angular range justifies these assumptions for the present problems. Polarization values lower than the theoretical ones were measured only at scattering angles where the theory predicts very narrow and high values of the spin polarization. Qualitative arguments show that intramolecular scattering very likely is responsible for the deviations found between theoretical and experimental polarization peaks. By means of the polarization of the scattered intensity one can easily decide how much of the scattered intensity comes from one part of the molecule and how much comes from the other part. 相似文献
5.
V. N. Petrov A. B. Ustinov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(3):395-400
The magnetic properties of the magnetite Fe3O4(110) surface have been studied by spin resolved Auger electron spectroscopy (SRAES). Experimental spin resolved Auger spectra
are presented. The results of calculation of Auger lines polarization carried out on the basis of electronic state density
are presented. Problems related to magnetic moments of bivalent (Fe2+) and trivalent (Fe3+) ions on the Fe3O4(110) surface are discussed. It is established that the deposition of a thin bismuth film on the surface results in significant
growth of polarization of iron Auger peaks, which is due to additional spin-orbit scattering of electrons by bismuth atoms. 相似文献
6.
We report on the first spin-resolved energy spectra for the emission of electrons during grazing scattering of 150 keV multicharged nitrogen ions from a magnetized Fe(001) surface. A substantial spin polarization for KLL Auger electrons emitted in the final stage of the neutralization sequence during the interaction of multicharged ions with a metal surface is observed. We conclude from our data that the projectile L shell is dominantly populated by electrons from the conduction band of the target. For low energy electrons we find an increase of their spin polarization with an increase of the projectile charge. 相似文献
7.
Y.S. Dedkov M. Fonin U. Rüdiger G. Güntherodt 《Applied Physics A: Materials Science & Processing》2006,82(3):489-493
The surface structure and electronic properties of ultrathin MgO layers grown on epitaxial Fe(110) films were investigated
at room temperature by means of electron diffraction, Auger electron spectroscopy, scanning tunneling microscopy, and spin-resolved
photoelectron spectroscopy. The spin polarization at the Fermi level (EF) of the Fe(110) film decreases sharply with increasing thickness of the MgO layer. This behavior arises from the formation
of a thin FeO layer at the MgO(111)/Fe(110) interface, as revealed by structural and spectroscopic investigations. The strong
attenuation of the intrinsic spin polarization is qualitatively attributed to the scattering of spin-polarized electrons at
the unoccupied d-orbitals of Fe2+.
PACS 68.35.-p; 68.55.-a; 73.20.r; 75.70.Cn; 79.60.-I 相似文献
8.
Magnetized iron foils of a thickness of 500 Å were transmitted by 60 keV electrons. The spin polarization of the electron beam was investigated by Mott scattering after transmission. No polarization effect was found. Since the lowest detectable polarization degree wasP=0·003 the atomic polarization cross section must be assumed to be smaller than 0·8·10?20cm2. This cross section is the sum of the spin exchange cross section and the spin dependent part of the total scattering cross section. If the electron binding energy is neglected, the spin depentend part of the total scattering cross section can be calculated from the theory of Møller scattering. In the case of our conditions-60 keV and an aperture of 10?3 radian-the calculated cross section is smaller than the experimental upper limit. In further experiments the electron beam was split into the energy spectrum by an electrostatic analyzer placed between the iron foil and the Mott scattering foil. In these measurements only small parts of the energy spectrum were investigated, however, even here no detectable polarization occured. 相似文献
9.
The influence of the Dresselhaus spin-orbit coupling on spin polarization by tunneling through a disordered semiconductor superlattice was investigated. The Dresselhaus spin-orbit coupling causes the spin polarization of the electron due to transmission possibilities difference between spin up and spin down electrons. The electron tunneling through a zinc-blende semiconductor superlattice with InAs and GaAs layers and two variable distance InxGa(1−x)As impurity layers was studied. One hundred percent spin polarization was obtained by optimizing the distance between two impurity layers and impurity percent in disordered layers in the presence of Dresselhaus spin-orbit coupling. In addition, the electron transmission probability through the mentioned superlattice is too much near to one and an efficient spin filtering was recommended. 相似文献
10.
We consider a mesoscopic ballistic structure with Rashba spin-orbit splitting of the electron spectrum. The ballistic region
is attached to the leads with a voltage applied between them. We calculate the edge spin density which appears in the presence
of a charge current through the structure due to the difference in populations of electrons coming from different leads. Combined
effect of the boundary scattering and spin precession leads to oscillations of the edge polarization with the envelope function
decaying as a power law of the distance from the boundary. The problem is solved with the use of scattering states. The simplicity
of the method allows us gain an insight into the underlying physics. We clarify the role of the unitarity of scattering for
the problem of edge spin accumulation. In case of a straight boundary it leads to exact cancellation of all long-wave oscillations
of the spin density. As a result, only the Friedel-like spin density oscillations with the momentum 2k
F
survive. However, this appears to be rather exceptional case. In general, the smooth spin oscillations with the spin precession
length recover, as it happens, e.g., for the wiggly boundary. We demonstrate also, that there is no relation between the spin
current in the bulk, which is zero in the considered case, and the edge spin accumulation. 相似文献
11.
Optical orientation of electrons was used to polarize the crystal lattice nuclei in quantum-size heterostructures and to study the effect of the conduction band spin splitting on the spin states of quasi-two-dimensional (2D) electrons drifting in an external electric field. High (~1%) nuclear polarization was registered using polarized luminescence and ODNMR in single GaAs/AlGaAs quantum wells. Measurement was made of the hyperfine interaction fields created by polarized nuclei on electrons and by electrons on nuclei. The spin-lattice relaxation of nuclei on the non-degenerate 2D electron gas was calculated. A comparison of the theoretical and experimental longitudinal relaxation times permitted the conclusion that the localized charge carriers are responsible for nuclear polarization in quantum wells in the temperature range of 2–77 K. A new effect has been studied, i.e. induction of an effective magnetic field acting on 2D electron spins when electrons drift in an external electric field in the quantum well plane. This effective field Beff is due to the spin splitting of the conduction band of 2D electrons. The paper discusses possible registration of an ODNMR signal when the field Beff is modulated by an electric current during optical orientation. 相似文献
12.
Akimov IA Dzhioev RI Korenev VL Kusrayev YG Sapega VF Yakovlev DR Bayer M 《Physical review letters》2011,106(14):147402
We report on optical orientation of Mn2+ ions in bulk GaAs subject to weak longitudinal magnetic fields (B≤100 mT). A manganese spin polarization of 25% is directly evaluated by using spin-flip Raman scattering. The dynamical Mn2+ polarization occurs due to the s-d exchange interaction with optically oriented conduction band electrons. Time-resolved photoluminescence reveals a nontrivial electron spin dynamics, where the oriented Mn2+ ions tend to stabilize the electron spins. 相似文献
13.
Consistency in formulation of spin current and torque associated with a variance of angular momentum
Based on the Noether's theorem, we develop systematically and rigorously the spin-dependent formulation of the conservation laws. The effect of the electronic polarization due to the spin-orbit coupling is included in the Maxwell equations. The polarization is related to the antisymmetric components of spin current, and it provides a possibility to measure the spin current directly. The variances of spin and orbit angular momentum currents imply a torque on the "electric dipole" associated with the moving electron. The dependencies of the torque on the polarization and the force on the motions of spin-polarized electrons in a two-dimensional electron gas with the Rashba spin-orbit coupling are discussed. 相似文献
14.
Numerical investigation of the electronic structure of a small closed quantum system fabricated on the two-dimensional electron gas forming on the interference between GaAs and AlxGa1-xAs is reported. The Kohn-Sham spin-density-fun ctional theory is applied. Self-consistent results show that the quantum system assumes unequal numbers of electrons for spin up and spin down because of the existence of bound states. The profiles of effective potential energies for spin up and spin down electrons are then found to be very different, which will result in different transmission coefficients. It is notable that this spin polarization is caused by the geometry of the nanostructure. 相似文献
15.
V. K. Kalevich A. Yu. Shiryaev E. L. Ivchenko A. Yu. Egorov L. Lombez D. Lagarde X. Marie T. Amand 《JETP Letters》2007,85(3):174-178
Conduction-electron spin polarization dynamics achieved by pulsed optical pumping at room temperature in GaAs1−x
N
x
alloys with a small nitrogen content (x = 2.1, 2.7, and 3.4%) is studied both experimentally and theoretically. It is found that the photoluminescence circular polarization
determined by the mean spin of free electrons reaches 40–45% and this giant value persists within 2 ns. Simultaneously, the
total free-electron spin decays rapidly with the characteristic time ≈ 150 ps. The results are explained by spin-dependent
capture of free conduction electrons on deep paramagnetic centers resulting in the dynamical polarization of bound electrons.
A nonlinear theory of spin dynamics in the coupled system of spin-polarized free and localized carriers has been developed
which describes the experimental dependencies, in particular, the electron spin quantum beats observed in a transverse magnetic
field.
The text was submitted by the authors in English. 相似文献
16.
动态核极化法(Dynamic Nuclear Polarization, DNP)是利用热平衡下的电子在磁场中的高自旋极化率转移到原子核自旋的技术,从而极大的提高原子核自旋极化率。多种动态极化靶材料已广泛的用于自旋物理散射实验。本文介绍一种简单实用,共同开发的日本山形大学DNP系统,包括超导磁场,氦4蒸发恒冷器,微波系统以及NMR核磁共振检测系统,测得中子靶材料氘带丁醇(D-butanol)中氘核的极化率在2.5T/1.3K达到+6.5%。 相似文献
17.
Dipl.-Phys H. F. Weiss 《Zeitschrift für Physik A Hadrons and Nuclei》1969,229(3-5):299-308
The elastic scattering of slow electrons from A, Kr and Hg is calculated by means of phase shift analysis. In addition to the Hartree potentials radial symmetric potentials are used simulating electron exchange and polarization of the shell electrons. It is found that spin polarization and differential cross-section are in relatively good agreement with the experimental results. 相似文献
18.
P. Lenisa 《Hyperfine Interactions》2000,127(1-4):481-484
The HERMES experiment at the electron ring of HERA at DESY studies the spin structure of proton and neutron by deep inelastic
scattering of polarized electrons off the nucleons of a highly polarized internal gas target. The target makes use of a storage
cell to increase the target density. The polarisation of a sample of the atoms in the cell is measured with a Breit-Rabi polarimeter.
A relaxation model based on the diffusion equation has been developed, which is used to calculate the corrections which are
needed to determine the absolute target polarization using the measured values.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
D. Conrath T. Heindorff A. Hermanni N. Ludwig E. Reichert 《Applied Physics A: Materials Science & Processing》1979,20(2):155-157
GaAs0.62P0.38 activated to negative electron affinity and irradiated with circularly polarized light of a wavelength shorter than approximately
680 nm emits electrons whose spins are mainly oriented antiparallel to the photon spins. At 650 nm a degree of electron spin
polarization around 40% is observed. The spectrum of spin polarization of the photoelectrons is similar to that known from
GaAs cathodes but is shifted to shorter wavelengths. 25 μA current of spin-polarized electrons were achieved with a 5 mW He-Ne
laser. 相似文献
20.
We present the first measurement of (e,2e) ionization cross sections for a laser oriented atomic target by spin polarized electrons. Cross sections are presented as a function of target orientation and polarization direction of the incident electron beam. This study provides insight into mechanisms by which angular momentum is transferred from the valence electron to the two final-state continuum electrons in both singlet and triplet spin channels, by comparing measurement with distorted wave Born approximation and the dynamically screened three Coulomb wave calculations. 相似文献